1. Field of the Invention
The present invention relates to a method and apparatus for transmitting data based on an available channel bandwidth when a channel access is performed in a wireless local area network (WLAN) system.
2. Description of the Related Art
In a wireless local area network (WLAN), an enhanced distributed channel access (EDCA) protocol and a distributed coordination function (DCF) protocol in which a station (STA) or an access point (AP) independently accesses a channel using a carrier sense multiple access/collision avoidance (CSMA/CA) protocol may be performed in contrast to a mobile communication system.
In a WLAN to which 802.11e standards are applied, when a channel access is started to transmit a frame using an EDCA method, a frame can be transmitted on a primary channel if the primary channel is idle for an arbitration interframe space (AIFS)+a back-off counter time. In order to use a secondary channel having a bandwidth of at least 20 megahertz (MHz) which is a size of a basic bandwidth, the channel access may be performed when a corresponding channel is in an idle state for a period of time greater than or equal to a priority interframe space (PIFS) immediately preceding the expiration of the backoff counter.
In general, the channel access may be performed using a 20/defer mode or a 40/defer mode in 11n of the WLAN. In the 20/defer mode, when a 20 MHz primary channel is available, a frame transmission may be performed. When the 20 MHz primary channel is unavailable, the frame transmission may be on standby until a channel enters the idle state. When an 802.11n STA performs a 40 MHz channel access in the 40/defer mode, a primary channel may be in an idle state during the arbitration interframe space (AIFS)+a back-off count time as described above. When a secondary channel is in an idle state for a period of time greater than or equal to the PIFS immediately preceding the expiration of the backoff counter, a frame transmission may be performed using a bandwidth of 40 MHz. When the secondary channel is not in the idle state for the period of time greater than or equal to the PIFS immediately preceding the expiration of the backoff counter, and the primary channel is available, the frame transmission may not be performed using a bandwidth of 20 MHz although the 20 MHz primary channel is available, and a back-off process may be executed again until the bandwidth of 40 MHz becomes available.
In a case of a 40/20/defer mode, while a utilization rate is relatively low, one of a method of using a bandwidth of 40 MHz, a method of using a bandwidth of 20 MHz, and a method of restarting a back-off may be used based on a channel state.